Import external txt with phyton
Try this (I am using Blender 2.81a)

import bpy
import os

# This gets text from file
filename = os.path.join(os.path.dirname(bpy.data.filepath), "info.txt")
f = open(filename, "r")
text_data = f.read()
f.close()

# Get your text object (object name here is 'Text')
obj = bpy.data.objects['Text']
obj.data.body = text_data # set text

```